Numerous oiling compounds are used as temporary corrosion preventatives to prevent the formation of rust on the surface of ferrous sheets, strips and other flat ware products during storage and transportation between the producer and the final user. These oiling compounds are, however, usually either not compatible with direct enameling of the steel surface or not pharmacologically acceptable for use in making food and beverage containers. Various anti-oxidation agents have also been available, many of which are compatible with direct enameling, but which are not pharmocologically safe. These various oiling compounds and anti-oxidation agents must, therefore, at least, when used in amounts which are effective to prevent commercially objectionable rusting of a steel surface, be subsequently removed from the surface by an expensive cleaning operation prior to enameling. Some compounds have been available such as dioctyl sebacate or analogous compounds which can be applied to tinplate, electrolytic chromium coated steel and blackplate to render the sheets mobile and scuff resistant. These compounds do not interfere with enameling in the small amounts in which they are used. However, these small amounts are not effective in preventing the appearance of rust on the metal surface and the use of greater amounts of the compounds is incompatible with direct enameling.
Certain compounds such as pentaerythrityl oleates, which are pharmocologically acceptable, have in the past been mixed with enameling compounds and applied to the surface of steel sheets during enameling of the sheets. During curing of the enamel layer the pentaerythrityl compounds migrate to the outer surface of the enamel layer where they serve as pharmocologically safe mobility inducing and anti-scuffing agents which allow the enameled sheets to be readily piled or stacked and subsequently withdrawn from the pile one at a time without damage to the enameled surface. Any prior corrosion preventative used directly on the surface of the original steel sheet for temporary rust prevention prior to enameling would still, however, have to be removed from the surface prior to the enameling step.
There has thus been a need for a temporary but effective rust preventative for application to the bare surface of steel sheets and the like which is both compatible with subsequent direct enameling and pharmocologically unobjectionable.
It is therefore an object of this invention to provide a composite steel sheet product which resists corrosion.
It is a further object of this invention to provide a corrosion resistant composite steel product which is directly enamelable.
It is also an object of this invention to provide a method for treating a steel sheet material so as to impart thereto corrosion resistance while maintaining direct enamelability.